Restriction Digests—Nature of Overhangs The unpaired single-stranded nucleotides left at DNA termini after certain restriction enzyme cuts are referred to as:

Introduction / Context:Restriction enzymes can generate either blunt ends or single-stranded overhangs. Overhangs provide complementarity that facilitates specific annealing and efficient ligation in recombinant DNA techniques.

Given Data / Assumptions:

• Some enzymes (EcoRI) produce 5' overhangs; others (KpnI) produce 3' overhangs.
• Overhangs enable base-pairing with compatible ends.
• Terminology distinguishes overhangs (“sticky ends”) from fully double-stranded “blunt ends.”

Concept / Approach:“Sticky ends” describes cohesive termini with unpaired nucleotides that can hydrogen-bond to complementary sequences. This property is exploited to directional-clone inserts into vectors cut with compatible enzymes.

Step-by-Step Solution:

Verification / Alternative check:Cloning manuals define sticky ends as overhangs that anneal via base pairing prior to ligase sealing of the backbone.

Why Other Options Are Wrong:

• Single strands: too generic; does not denote cohesive ends specifically.
• Restriction fragments: includes blunt- and sticky-ended pieces.
• Ligases: enzymes that seal nicks; not DNA ends.
• Polylinkers: engineered multiple-cloning sites in vectors.

Common Pitfalls:Confusing overhang type (5' vs 3') with the general property “sticky.”

Final Answer:Sticky ends